GDI+ Shapes: Rectangles and Squares

	GDI+ Shapes: Rectangles and Squares

Description

A rectangle is a geometric figure made of four sides that compose four right angles. To draw a rectangle, you can either specify the Rectangle value that encloses it, or you can define its location and its dimensions. To draw a rectangle that is enclosed in a Rectangle value, you can use the following version of the Graphics.DrawRectangle() method:

Public Sub DrawRectangle(pen As Pen, rect As Rectangle)

Remember that such a rectangle object can be illustrated as follows:

After defining a Rectangle variable, you can pass it to the method. Here is an example:

Imports System.Drawing
Imports System.Windows.Forms

Module Exercise

    Public Class Starter
        Inherits Form

        Dim components As System.ComponentModel.Container

        Public Sub New()
            InitializeComponent()
        End Sub

        Public Sub InitializeComponent()

        End Sub

        Private Sub FormPaint(ByVal sender As Object, _
                              ByVal e As PaintEventArgs) _
                              Handles MyBase.Paint

            Dim penCurrent As Pen = New Pen(Color.Red)
            Dim Rect As Rectangle = New Rectangle(20, 20, 248, 162)

            e.Graphics.DrawRectangle(penCurrent, Rect)

        End Sub
    End Class

    Function Main() As Integer

        Dim frmStart As Starter = New Starter

        Application.Run(frmStart)

        Return 0
    End Function

End Module

Remember that you can also define a Pen and/or a Rectangle objects in the parentheses of the method:

Private Sub FormPaint(ByVal sender As Object, _
                              ByVal e As PaintEventArgs) _
                              Handles MyBase.Paint

            Dim penCurrent As Pen = New Pen(Color.Red)
            Dim Rect As Rectangle = New Rectangle(20, 20, 248, 162)

            e.Graphics.DrawRectangle(New Pen(Color.Red), _
                   New Rectangle(20, 20, 248, 162))

End Sub

This would produce:

A Rectangle Drawn From a Rectangle Value

It is (very) important to remember that the third argument of the Rectangle represents its width (and not its right) value and the fourth argument represents its height (and not its bottom) value. This is a confusing fact for those who have programmed in GDI: GDI+ defines a Rectangle differently than GDI. In fact, to determine the location and dimensions of a rectangle to draw, the Graphics class provides the following versions of the DrawRectangle() method:

Public Sub DrawRectangle(pen As Pen, x As Integer, _
		          y As Integer, width As Integer, _
		          height As Integer)
Public Sub DrawRectangle(pen As Pen, x As Single, _
		          y As Single, width As Single, _
		          height As Single)

This time, the rectangle is represented by its location with a point at (x, y) and its dimensions with the width and height argument. This can be illustrated in a Windows coordinate system as follows:

Based on this, the earlier rectangle can also be drawn with the following:

Private Sub FormPaint(ByVal sender As Object, _
                              ByVal e As PaintEventArgs) _
                              Handles MyBase.Paint

            e.Graphics.DrawRectangle(New Pen(Color.Red), 20, 20, 248, 162)

End Sub

A square is a rectangle whose four sides are equal.

Practical Learning: Drawing a Rectangle

Start Microsoft Visual Basic and create a new Windows Application named WeeklySales1

Design the form as follows:

Control	Name	Text
Label		Monday
Label		Tuesday
Label		Wednesday
Label		Thursday
Label		Friday
TextBox	txtMonday	0
TextBox	txtTuesday	0
TextBox	txtWednesday	0
TextBox	txtThursday	0
TextBox	txtFriday	0
Button	Generate	btnGenerate

Double-click an unoccupied area of the form and change the file as follows:

Public Class Form1

    Private graphDrawingArea As Graphics
    Private bmpDrawingArea As Bitmap

    Private Sub Form1_Load(ByVal sender As System.Object, _
                           ByVal e As System.EventArgs) _
                           Handles MyBase.Load
        bmpDrawingArea = New Bitmap(Width, Height)
        graphDrawingArea = Graphics.FromImage(bmpDrawingArea)
    End Sub
End Class

In the Method Name combo box, select Paint and implement its event as follows:

Private Sub Form1_Paint(ByVal sender As Object, _
                 ByVal e As System.Windows.Forms.PaintEventArgs) _
                        Handles Me.Paint
        e.Graphics.DrawImage(bmpDrawingArea, 0, 0)
End Sub

In the Class Name combo box, select btnGenerate

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnGenerate_Click(ByVal sender As Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnGenerate.Click
        Dim monday As Integer
        Dim tuesday As Integer
        Dim wednesday As Integer
        Dim thursday As Integer
        Dim friday As Integer

        Try
            monday = CInt(txtMonday.Text) / 100
        Catch
            MsgBox("Invalid sales on Monday")
            txtMonday.Text = "0"
        End Try

        Try
            tuesday = CInt(txtTuesday.Text) / 100
        Catch
            MsgBox("Invalid sales on Tuesday")
            txtTuesday.Text = "0"
        End Try

        Try
            wednesday = Integer.Parse(txtWednesday.Text) / 100
        Catch
            MsgBox("Invalid sales on Wednesday")
            txtWednesday.Text = "0"
        End Try

        Try
            thursday = CInt(txtThursday.Text) / 100
        Catch
            MsgBox("Invalid sales on Thursday")
            txtThursday.Text = "0"
        End Try

        Try
            friday = CInt(txtFriday.Text) / 100
        Catch
            MsgBox("Invalid sales on Friday")
            txtFriday.Text = "0"
        End Try

        graphDrawingArea.Clear(BackColor)

        graphDrawingArea.DrawRectangle(New Pen(Color.Red), _
                            txtMonday.Left + 10, _
                            300 - monday, 40, monday)
        graphDrawingArea.DrawRectangle(New Pen(Color.Blue), _
                            txtTuesday.Left + 10, _
                            300 - tuesday, 40, tuesday)
        graphDrawingArea.DrawRectangle(New Pen(Color.Fuchsia), _
                            txtWednesday.Left + 5, _
                            300 - wednesday, 40, wednesday)
        graphDrawingArea.DrawRectangle(New Pen(Color.Brown), _
                            txtThursday.Left + 5, _
                            300 - thursday, 40, thursday)
        graphDrawingArea.DrawRectangle(New Pen(Color.Turquoise), _
                            txtFriday.Left + 5, _
                            300 - friday, 40, friday)

        graphDrawingArea.DrawRectangle(New Pen(Color.Black), _
                            10, 300, Width - 30, 1)
        Invalidate()
End Sub

Execute the application and test the form
After using it, close the form

A Series of Rectangles

The DrawRectangle() method is used to draw one rectangle. If you plan to draw many rectangles, you can proceed in one step by using the Graphics.DrawRectangles() method. It comes in two versions whose syntaxes are:

Public Sub DrawRectangles(pen As Pen, rects As Rectangle() )
Public Sub DrawRectangles(pen As Pen, rects As RectangleF())

This method requires an array of Rectangle or RectangleF values. When executed, it draws individual rectangles using each member of the array as its own rectangle. Here is an example:

Private Sub FormPaint(ByVal sender As Object, _
                              ByVal e As PaintEventArgs) _
                              Handles MyBase.Paint

            Dim penCurrent As Pen = New Pen(Color.Red)
            Dim Rect As Rectangle() =  _
			New Rectangle(20, 20, 120, 20), _
                                    	New Rectangle(20, 50, 120, 30), _
                     		New Rectangle(20, 90, 120, 40), _
                     		New Rectangle(20, 140, 120, 60)}

            e.Graphics.DrawRectangles(penCurrent, Rect)

End Sub

This would produce:

Practical Learning: Drawing a Series of Rectangles

Start a new Windows Application named YearlySales1

Design the form as follows:

Control	Name	Text
GroupBox		Current Year's Sales
Label		1st Qtr
Label		2nd Qtr
Label		3rd Qtr
Label		4th Qtr
TextBox	txtCurrentQtr1	0
TextBox	txtCurrentQtr2	0
TextBox	txtCurrentQtr3	0
TextBox	txtCurrentQtr4	0
Button	Close	btnClose
GroupBox		Previous Year's Sales
Label		1st Qtr
Label		2nd Qtr
Label		3rd Qtr
Label		4th Qtr
TextBox	txtPreviousQtr1	0
TextBox	txtPreviousQtr2	0
TextBox	txtPreviousQtr3	0
TextBox	txtPreviousQtr4	0
Button	Generate	btnGenerate
Label		_________ Legend _________
Label	lblCurYear	This Year's Sales
Label	lblLastYear	Last Year's Sales

Double-click an unoccupied area of the form and change the file as follows:

Public Class Form1

    Private graphDrawingArea As Graphics
    Private bmpDrawingArea As Bitmap

    Private Sub Form1_Load(ByVal sender As System.Object, _
                           ByVal e As System.EventArgs) _
                           Handles MyBase.Load
        bmpDrawingArea = New Bitmap(Width, Height)
        graphDrawingArea = Graphics.FromImage(bmpDrawingArea)
    End Sub
End Class

In Method Name combo box, select Paint and implement its event as follows:

Private Sub Form1_Paint(ByVal sender As Object, _
                            ByVal e As System.Windows.Forms.PaintEventArgs) _
                            Handles Me.Paint
        e.Graphics.DrawImage(bmpDrawingArea, 0, 0)
End Sub

In the Class Name combo box, select btnGenerate

In the Method Name combo box, select Click and implement the event as follows:

Private Sub btnGenerate_Click(ByVal sender As Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnGenerate.Click
        Dim curQtr1 As Integer
        Dim curQtr2 As Integer
        Dim curQtr3 As Integer
        Dim curQtr4 As Integer
        Dim prvQtr1 As Integer
        Dim prvQtr2 As Integer
        Dim prvQtr3 As Integer
        Dim prvQtr4 As Integer

        ' Retrieve the values of the current year's sales
        Try
            curQtr1 = CInt(txtCurrentQtr1.Text) / 100
        Catch
            MsgBox("Invalid value for the first quater")
            curQtr1 = 0
        End Try

        Try
            curQtr2 = CInt(txtCurrentQtr2.Text) / 100
        Catch
            MsgBox("Invalid value for the second quater")
            curQtr2 = 0
        End Try

        Try
            curQtr3 = CInt(txtCurrentQtr3.Text) / 100
        Catch
            MsgBox("Invalid value for the third quater")
            curQtr3 = 0
        End Try

        Try
            curQtr4 = CInt(txtCurrentQtr4.Text) / 100
        Catch
            MsgBox("Invalid value for the fourth quater")
            curQtr4 = 0
        End Try

        ' Create an array of Rectangle objects for the current year
        Dim rectCurrentYear As Rectangle() = { _
                       New Rectangle(txtCurrentQtr1.Left + 20, _
                                  380 - curQtr1, 40, curQtr1), _
                       New Rectangle(txtCurrentQtr2.Left + 20, _
                                  380 - curQtr2, 40, curQtr2), _
                       New Rectangle(txtCurrentQtr3.Left + 20, _
                                  380 - curQtr3, 40, curQtr3), _
                       New Rectangle(txtCurrentQtr4.Left + 20, _
                                  380 - curQtr4, 40, curQtr4)}

        ' Retrieve the values of last year's sales
        Try
            prvQtr1 = CInt(txtPreviousQtr1.Text) / 100
        Catch
            MsgBox("Invalid value for the third quater")
            prvQtr1 = 0
        End Try

        Try
            prvQtr2 = CInt(txtPreviousQtr2.Text) / 100
        Catch
            MsgBox("Invalid value for the third quater")
            prvQtr2 = 0
        End Try

        Try
            prvQtr3 = CInt(txtPreviousQtr3.Text) / 100
        Catch
            MsgBox("Invalid value for the third quater")
            prvQtr3 = 0
        End Try

        Try
            prvQtr4 = CInt(txtPreviousQtr4.Text) / 100
        Catch
            MsgBox("Invalid value for the third quater")
            prvQtr4 = 0
        End Try

        ' Create an array of Rectangle objects for the previous year
        Dim rectPreviousYear As Rectangle() = { _
                       New Rectangle(txtPreviousQtr1.Left + 30, _
                                  380 - prvQtr1, 40, prvQtr1), _
                       New Rectangle(txtPreviousQtr2.Left + 30, _
                                  380 - prvQtr2, 40, prvQtr2), _
                       New Rectangle(txtPreviousQtr3.Left + 30, _
                                  380 - prvQtr3, 40, prvQtr3), _
                       New Rectangle(txtPreviousQtr4.Left + 30, _
                                  380 - prvQtr4, 40, prvQtr4)}

        ' In case the user has changed the values,
        ' erase the previous chart
        graphDrawingArea.Clear(BackColor)

        ' Draw the chart for the previous year first to send it back
        graphDrawingArea.DrawRectangles(New Pen(Color.Blue), _
                         rectPreviousYear)
        ' Draw the chart for the current year in front
        graphDrawingArea.DrawRectangles(New Pen(Color.Red), _
                         rectCurrentYear)

        ' Draw the small rectangles of the legend
        graphDrawingArea.DrawRectangle(New Pen(Color.Blue), _
                        lblCurYear.Left - 30, _
                        lblCurYear.Top, 14, 10)
        graphDrawingArea.DrawRectangle(New Pen(Color.Red), _
                        lblLastYear.Left - 30, _
                        lblLastYear.Top, 14, 10)

        graphDrawingArea.DrawRectangle(New Pen(Color.Black), _
                         25, 380, Width - 220, 1)
        Invalidate()
End Sub

In the Class Name combo box, select btnClose

In the Method Name combo box, select Click and implement its event as follows:

Private Sub btnClose_Click(ByVal sender As Object, _
                               ByVal e As System.EventArgs) _
                               Handles btnClose.Click
        End
End Sub

Execute the application and test the form
After using it, close the form

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